基于有限单元法的多间隙耦合齿轮传动系统非线性动态特性分析

针对齿轮传动系统的动态传递误差、单双边冲击状态、脱齿、拍击及混沌现象等复杂非线性动力学问题,在同时考虑齿侧间隙、轴承间隙、时变啮合刚度及齿面摩擦等非线性特性的基础上,首次提出一种基于有限单元法的多间隙耦合齿轮传动系统的非线性动态特性分析方法。以某单级斜齿轮传动系统为例,利用大型通用有限元分析软件AN-SYS/LS-DYNA建立耦合系统动力学模型,分析支撑状态下耦合系统的非线性动态特性,研究了不同转速及负载力矩对耦合系统非线性动态特性的影响规律。结果表明有限单元法能在满足高精度分析的条件下求解各种复杂工况的齿轮系统非线性动力学问题,为进一步研究齿轮传动系统非线性动力学问题提供有力工具。     

Numerical investigation of onset and evolution of LVI damages in Carbon–Epoxy plates

In order to study the onset and the evolution of low velocity impact damages in Carbon–Epoxy plates, a numerical investigation has been led. A detailed finite element model has been created by using the finite element code Abaqus® which, thanks to the different implemented algorithms, allowed considering both intra-laminar and inter-laminar failure criteria.In particular, the numerical modelling technique of such failure criteria allowed predicting delamination growth, by using special purpose-elements (cohesive elements) and fiber and matrix failure, by using Hashin criteria.Moreover, with the aim to reduce the required CPU time, a global/local finite element modelling approach has been proposed.For validation purpose, numerical results have been compared with data from two sessions of experimental impact tests. The considered impact energy values are 6 J, 10 J and 13 J respectively.     

用虚裂纹模型研究混凝土裂缝扩展的边界单元法

本文将虚裂纹模型引入边界元法中,从而推出了用虚裂纹模型研究混凝土裂缝扩展过程的边界元法。由于边界元法在解决断裂问题时的优势,使得该法成为分析混凝土裂缝的有效方法之一。文中利用自编程序,给出了算例。     

Nonlocal anisotropic damage model and related computational aspects for quasi-brittle materials

A three-dimensional damage model with induced damage anisotropy is proposed for quasi-brittle materials such as concrete. The thermodynamics framework is used, considering then a single second-order tensorial damage variable whatever the intensity and the sign of the loading. The quasi-unilateral conditions of micro-cracks closure are written on the hydrostatic stress only. Altogether with the consideration of damage laws ensuring a damage rate proportional to the positive part of the strain tensor this is sufficient to model a strongly different behavior due to damage in tension and in compression. A proof of the positivity of the intrinsic dissipation due to such an induced anisotropic damage is given.An efficient scheme for the implementation of the damage model in commercial Finite Element codes is then detailed and numerical examples of structural failures are given. Plain concrete, reinforced and pre-stressed concrete structures are computed up to high damage level inducing yielding of the reinforcement steels. Local and nonlocal computations are performed.A procedure for the control of rupture is proposed. It is a key point making the computations with anisotropic damage truly efficient.     

具有摩擦阻尼结点之结构动力分析

本文将增量谐波平衡法(Incremental Harmonic Balance Method, I. H. B Method)结合组抗方法用于分析具有摩擦结点之结构稳态动力响应。这方法之主要优点是能将线性结构与摩擦结点分开来考虑。当摩擦结点之自由度远小于线性结构之自由度时,计算是很经济的。发展了一个分析这种系统之计算程序可与一般有限元结构分析程序如SAPV或ADINA相连,作为后处理程序。     

混凝土构件软化分析的边界元法

本文在混凝土构件的软化分析中采用了粘性裂纹模型,使用直接边界元子域法研究并讨论了构件中裂纹开展所引起的结构软化和失稳情形,相应的增量迭代算法被给出。文中的数值算例表明了上述方法的有效性。     

A robust numerical approach for the simulation of skin–stringer debonding growth in stiffened composite panels under compression

In this paper, a numerical study on skin–stringer debonding growth in stiffened composite panels has been carried out. A novel numerical methodology is proposed here to investigate the compressive behaviour of a stiffened composite panel in the presence of skin–stringer partial separation. The novel numerical methodology, able to overcome the mesh size and time increment dependency of the standard Virtual Crack Closure Technique (VCCT), is an evolution of a previously developed and tested numerical approach for the circular delaminations growth. The enhancements, with respect to the previously developed approach, rely mainly in the capability to deal with the different defect shapes characterising a skin–stringer debonding. The proposed novel methodology has been implemented in a commercial finite element platform and tested over single stiffener composite panels. The effectiveness of the suggested numerical methodology, in predicting the compressive behaviour of stiffened panels with skin stringer debondings, has been preliminary confirmed by comparisons, in terms of load versus applied displacement and debonding size at failure, with literature experimental data and numerical results obtained with the standard VCCT approach.     

汽车动力总成悬置骨架的拓扑优化设计

以某商用车动力总成的悬置骨架为分析对象,基于变密度法建立拓扑优化的数学模型及其求解方法;运用有限元软件Hyperworks中的Optistruct模块将拓扑优化方法应用到该商用车动力总成的悬置骨架结构设计中,对单工况下的骨架结构进行优化设计。根据优化的结果并结合生产经验,设计出新悬置骨架的结构。最后用ABAQUS软件对悬置总成进行应力、变形和体积的计算。结果表明,经过优化的悬置骨架安全性能得到提高,重量减轻。     

Homogenization of transient heat transfer problems for some composite materials

The article presented is devoted to the homogenization of transient heat transfer problems in some composite materials. The mathematical model used in the FEM computation is based on the effective modules method introduced for periodic composites. The effective heat conductivity is calculated in the closed form; effective heat capacity and mass density for the composite are obtained by simple spatial averaging. Such a homogenization scheme makes it possible to significantly simplify the numerical analysis of transient heat phenomena in various types of composites. Computational experiments performed using symbolic mathematics show the variability of effective heat conductivity for 2D and 3D composites as a function of the reinforcement volume ratio, of composite components conductivity coefficients as well as of the probabilistic moments of material properties versus volume ratio. Finally, using the Finite Element Method program, the comparison of transient heat transfer problem for the real and homogenized composites models is carried out.     

Evaluation of directional mesh bias in concrete fracture simulations using continuum damage models

In the present comparative study, we investigate the influence of directional mesh bias on the results of failure simulations performed with isotropic and anisotropic damage models. Several fracture tests leading to curved crack trajectories are simulated on different meshes. The isotropic damage model with a realistic biaxial strength envelope for concrete is highly sensitive to the mesh orientation, even for fine meshes. The sensitivity is reduced if the definition of the damage-driving variable (equivalent strain) is based on the modified von Mises criterion, but the corresponding biaxial strength envelope is not realistic for concrete. The anisotropic damage models used in this study capture reasonably well arbitrary crack trajectories even if the biaxial strength envelope remains close to typical experimental data. Their superior performance can be at least partially attributed to their ability to capture dilatancy under shear, which is revealed by a comparative analysis of the behavior of individual models under shear with restricted or free volume expansion.     

Dehydration creep of concrete at high temperatures

In this paper, a new approach for modeling the transient component of the load induced thermal deformation is proposed in order to predict the concrete behavior when subjected to high temperatures with a concomitant applied load. This component is conventionally referred to as transient creep strain. In this approach, the transient creep strain is split into a drying creep component and a newly introduced dehydration creep strain. The former is related to the evolution of the hygrometric state of the material, while the latter is related to the material dehydration which results from the heating induced chemical transformations. Therefore, a dehydration variable is defined and then introduced as a driving variable of the transient creep for temperatures exceeding 105°C. This thermo-hydro-damage model is implemented using a finite element code and␣numerical simulations are performed and compared to experimental findings in order to assess the predictive character of the proposed model.

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Résumé Dans cet article, une nouvelle approche pour la modélisation de la composante transitoire de la déformation thermique induite sous charge est proposée afin de prédire le comportement du béton à hautes températures. Cette composante est conventionnellement connue sous le nom du fluage thermique transitoire. Dans cette approche, le fluage thermique transitoire est décomposé en fluage de dessiccation et en une composante, nouvellement introduite, de fluage de déshydratation. La première composante est due à l’évolution hygrométrique du matériau tandis que la deuxième est due à la déshydratation du matériau qui résulte des transformations chimiques induites par l’augmentation de la température. Par conséquent, une variable de déshydratation est définie et est introduite comme une variable régissant le fluage thermique transitoire lorsque la température dépasse 105°C. Ce modèle thermo-hydro-endommageable est implémenté dans un code aux éléments finis. Des simulations numériques sont effectuées et comparées à des résultats expérimentaux pour analyser les capacités prédictives du modèle proposé.

     

高层筒体结构的二阶分析

本文用有限元线法(FEMOL)对高层筒体结构进行二阶分析。采用连续化方法将实际框筒结构等效为正交各向异性折板结构,用有限元线法进行单元分析并集成,用最小势能原理建立二阶分析的四阶常微分方程组,调用高质高效的常微分方程求解器COLSYS求解。